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2002 IEEE NSS Dmitri Denisov, Fermilab
Forward Muon System for the D0 Experiment
Presented by Dmitri DenisovFermilab
For the D0 Collaboration
644 members73 institutions18 countries
D0 Note 4061November 2002
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2002 IEEE NSS Dmitri Denisov, Fermilab
Fermilab Tevatron Upgrade
Tevatron Run 1 (1992-1996) produced reach harvest of interesting physics results, including top quark discovery
In order to continue studies at the energy frontier Tevatron underwent serious upgrade in 1997-2001
factor of ~10 higher luminosity
factor of ~10 smaller bunch spacing
Physics goals for Tevatron Run 2:
precision studies of weak bosons, top, QCD, B-physics
searches for Higgs, supersymmetry, extra dimensions, other new phenomena
4.82.32.5Interactions / xing
1323963500Bunch xing (ns)
10517.33.2 Ldt (pb-1/week)
5.2 10328.6 10311.6 1030Typical L (cm-2s-1)
1.961.961.8s (TeV)
140 10336 366 6Bunches in Turn
Run 2bRun 2aRun 1b
Run 1 Run 2a Run 2b 0.1 fb-1 24 fb-1 15 fb-1
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2002 IEEE NSS Dmitri Denisov, Fermilab
Challenges for the Tevatron Run 2 Detectors
In order to fully exploit Tevatron capabilities in Run 2 D0 detector has been substantially upgraded
smaller bunch crossing of 132ns (vs 3.1s) required replacement of electronics as well as some of the slow detectors
higher luminosity provides higher radiation fluxes and requires more radiation hard detectors
higher event rate requires better trigger systems in order to select only ~10-5 of the interactions which can be written to tapes
new detectors have been added in order to improve detection of displaced vertices and provide momentum measurement in the central region
Forward muon system of the D0 detector covers rapidity region between 1.0 and 2.0 and has been fully redesigned for Run 2
separated functions of muon tracking and trigger detectors fast detectors with internal resolution time below 60ns radiation hard detectors detectors capable of operating in the magnetic field of the muon toroid and central
solenoid time and coordinate resolution provide efficient muon detection and backgrounds
suppression
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2002 IEEE NSS Dmitri Denisov, Fermilab
D0 Detector for Run IIForward MDT Layers C B A
A- Counters
Pixel Counter LayersA B C
New 2T Solenoid
PDT Chambers C B A
Outer Counters
Shielding Shielding
PreshowerFiber Tracker
Silicon Tracker
Electronics
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2002 IEEE NSS Dmitri Denisov, Fermilab
Forward Muon System
Forward muon system consists of the following major elements
shielding around Tevatron beam pipe
provides factor of ~100 reduction in backgrounds
trigger system based on 3 layers of scintillation trigger counters
4608 scintillation counters with ~1ns time resolution
tracking system based on 3 layers of mini-drift tubes
50,000 wires assembled in 8 wires extrusion assemblies
maximum drift time is 60ns coordinate resolution is 0.7mm
Forward scintillationcounters
Shielding
Mini-drift tubes
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2002 IEEE NSS Dmitri Denisov, Fermilab
Shielding
There are two major sources of backgrounds(non-muon) hits in muon detectors at hadron colliders
background particles coming from the accelerator tunnel
background particles originated in interactions of p-pbar collision products propagating at small angles with accelerator and detector equipment
Both of these backgrounds can be substantially reduced by placing shielding around beam pipe
consists of 3 layers 50 cm of steel - absorb hadrons and e/gamma 12 cm of polyethylene - absorb neutrons 5 cm of lead - absorb gamma rays
calculations based on GEANT/MARS codes demonstrate reduction in particle fluxes for shielded/unshielded detectors by a factor of 50-100
Run 1 muon detector occupancies have been in the 5-10% level
Run 2 muon detector occupancies are in the 0.05-0.1% level in good agreement with calculations
use of detectors less sensitive to backgrounds (high time resolution, small sensitive volume, etc.) provides advantages as well
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2002 IEEE NSS Dmitri Denisov, Fermilab
Shielding
Effect of the shielding on background fluxes:factor of 50-100 reduction
Without Shielding With Shielding
Hadron
e/gamma
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2002 IEEE NSS Dmitri Denisov, Fermilab
Trigger Scintillation Counters
3 planes of ~10x10m2 on both sides of the interaction region
Counters arranged in R- geometry matching central fiber tracker trigger
Total number of counters 4608 Major specifications
fine segmentation time resolution of ~1ns to separate
tracks coming from interaction region from cosmic and accelerator tunnel
low radiation aging operation in magnetic field up to
~350Gs Simple and reliable design has been
developed based on 12mm thick Bicron 404A
scintillator light collection is performed using
WLS bars fast 25mm diameter phototubes are
used for light collection
10x10m2 plane of counters assembled in“fish scale” design in the collision hall
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2002 IEEE NSS Dmitri Denisov, Fermilab
Trigger Scintillation Counters
Cut to shape 404A scintillator with two Kumarin WLS bars attached collect light on the 25mm photocathode of 115M (MELZ)
phototube•Tyvek wrapping is used for better light collection
•Counters sizes are from 10x10cm2 to 1x1m2
•Average number of phe for large counters is 60•Time resolution is 0.5-1ns depending on counter size
limited by photoelectron statistics and amplitude fluctuations (single threshold discriminator)
•Amplitude response uniformity is ~10%
Radiation aging for 15fb-1 integrated luminosity
(Run II Tevatron goal)
Pair Kumarin(WLS)+404A(Scintillator) demonstrates 10% light loss for 20krad irradiation. We expect doses for the hottest regions to be well below 1krad (15fb-1)
Phototube 115M losses 10% of gain for anode accumulated charge of 100C (15fb-1). This could be easily compensated by HV adjustment
Counter Design
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2002 IEEE NSS Dmitri Denisov, Fermilab
Magnetic Shielding
Magnetic shielding is provided with 1.2mm thick mu-metal 3mm or 6mm tick soft iron
shield transverse to tube axis field has
no effect up to ~700Gs field parallel to the tube affects
phototubes 3mm iron shield (closed
circles): 10% gain loss at 250Gs
– used in layers outside muon toroid
6mm iron shield (open circles): 10% gain loss at 350Gs
– used in layer inside muon toroid
LED tests with/without field less then 1-2% effect for all
4608 tubes
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2002 IEEE NSS Dmitri Denisov, Fermilab
Counters Performance During Data Taking
During collider data collection performance of all counters is monitored efficiency of individual planes and counters based on reconstructed muon tracks
stable above 99% gain of all phototubes with respect to reference calibration set using LED system
peak position stable within ~2% over one year of operation typical variations in the gain do not exceed ~5%
timing characteristics peak of LED pulse is stable within 0.5ns over a year of operation peak and width of the timing spectra for muon tracks
Total number of “dead” counters after 1 year of operation is 5 (0.1%)1 year LED timing stabilityTiming peak for muon tracks
=1.8ns =0.5ns
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2002 IEEE NSS Dmitri Denisov, Fermilab
Forward Muon Tracking Detector
Forward muon tracking detector is based on mini-drift tubes
1x1cm2 drift cell 8 cell aluminum extrusion comb with 0.7mm
thick walls (to reduce dead zones) stainless steel cover and PVC sleeve provides
electrical field configuration and gas tight volume
•Tubes length vary between 1m and 6m•50mm gold plated tungsten wire is supported every meter•Total number of wires in the system is 50,000•Tubes are assembled into 8 octants per layer with wires parallel to magnetic field lines•There are 4 planes of wires in layer before toroid and 3 planes of wires in each of two layers after toroid
• muon has 10 hits on track average
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2002 IEEE NSS Dmitri Denisov, Fermilab
Working Gas for Mini-drift Tubes
We are using CF4(90%)+CH4(10%) gas mixture non-flammable very fast re-circulation with small losses (~5%)
reduces gas cost no radiation aging wide 100% efficiency mip platou
2.9kV-3.4kV Time-to-distance dependence has been
measured and simulated maximum drift time for tracks
perpendicular to the plane is ~40ns maximum dirft time for 45 degree tracks
is ~60ns Coordinate resolution of the mini-drift tube
system is defined by electronics TDC bin is 19ns (cost driven) =0.7mm starts affect “muon system only”
coordinate resolution for muon momentum above 50GeV/c
Accumulated charge for 15fb-1 is estimated at 30mC/cm
Aging test with Sr90 r/a source demonstrates no aging effects
up to 2C/cmWith large safety factor mini-drift
tubes radiation aging is not an issue
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2002 IEEE NSS Dmitri Denisov, Fermilab
Mini-drift Tubes Performance
During data collection many parameters of the mini-drift tubes are monitored
gas flow ~32 tubes are connected in
serial with input/output flow monitoring
high voltage values and currents all 50,000 wires operates at the
same high voltage of 3.25kV individual planes efficiency using
reconstructed muon segments typical efficiency is in the range
above 99% plane coordinate accuracy using
reconstructed segments Reliability
total number of disabled wires 0.3% after commissioning
– dead or noisy increase in number of disabled wires
is less then 0.1% per year of operation
Coordinate resolution of mini-drift tube plane
based on local segment reconstruction
RMS=0.7mm
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2002 IEEE NSS Dmitri Denisov, Fermilab
Forward Muon System Performance
Low occupancy of the forward muon detectors due to well designed shielding and use of fast detectors proved to be very low
at the 0.05%-0.1% level simple and reliable muon triggering
after Level 1 trigger (scintillation counters only) 50% of events have good muon reconstructed off-line
after Level 2 trigger (mini-drift tubes and scintillation counters) 80% of events have good track reconstructed off-line
– writing to tapes background free samples
simple and background free muon off-line reconstruction
High reliability of forward muon detectors provided above 99% “up-time” during physics data collection
Based on efficient muon hits detection, triggering, and reconstruction D0 forward muon system is providing data for wide spectrum of physics studies at the energy frontier at the Tevatron
Some important issues like alignment, electronics, triggering, reconstruction are not addressed due to limited talk time
M = 3.08 0.04 GeV
= 0.78 0.08 GeV
Single Muon Event
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2002 IEEE NSS Dmitri Denisov, Fermilab
Summary: D0 Forward Muon System
D0 experiment developed and constructed multi-layer steel+poly+lead shielding which reduced background fluxes on the muon detectors by a factor of 50-100
reduction in detectors aging, trigger rates, fake tracks Separation of triggering and tracking capabilities in the D0
forward muon system provides background free muon samples to be written to tapes
Forward muon trigger system based on 4608 scintillation counters
simple and reliable counter design for counters from 10x10cm2 to 1x1m2
time resolution of ~1ns provides above 60 phe per mip radiation hard to well above 100kRad phototube magnetic shield provides reliable operation up
to 350Gs Forward muon tracking system
50,000 wires of mini-drift tubes with 1x1cm2 drift cells and length up to 6m
modular extrusion based tube design CF4(90%)+CH4(10%) gas mixture
fast, 60ns max drift time non-flammable radiation hard above 2C/cm wide HV operating plateau of 0.5kV
All system elements reached or exceeded Run II specifications and operate smoothly during over a year of data taking